Conventional semiconductor package substrates typically include at least one core layer impregnated in a dielectric material to provide mechanical rigidity to the substrate. Latest trends of electronic devices such as mobile phones, mobile internet devices (MIDs), multimedia devices and computer notebooks demand for slimmer and lighter designs. Coreless substrates are adopted for fabrication of components in such electronic devices to enable a thinner profile of the components. The thickness of coreless substrates can be, for example, as little as approximately 25% of the thickness of cored substrates.
However, coreless substrates are more susceptible to warpage problem during Surface Mount Technology (SMT) processes compared to conventional substrates with core layers. SMT processes typically involve subjecting package substrates to heating and cooling which in turn create expansion and contraction of the substrate. The difference in coefficient of thermal expansion (CTE) of the various materials forming the substrate results in different rates of expansion and contraction and hence stress in the substrate. The resulting stress warps the substrate and causes manufacturing problems during component package assembly as well as during surface mount process at Original Equipment Manufacturers (OEMs). Unlike conventional substrates, coreless substrates do not have a core layer to provide flexural rigidity against package warpage. It is known that materials such as glass cloth and glass fibers are impregnated in the dielectric material of coreless substrates to provide flexural rigidity.